Dementia with Lewy bodies (DLB) is a devastating neurodegenerative disease. Cortical Lewy body pathology (LBP), which is the pathological substrate of DLB, is observed in 10%-30% of brains in most autopsy series of dementia patients. At the molecular level, LBP consists of aberrant deposits of alpha-synuclein (alpha-SN) protein and there is evidence that increased alpha-SN gene dosage is seen in some cases of DLB. The biochemical pathways that contribute to LBP are poorly understood and our overall goal is to help fill this knowledge gap. Men have strongly (~three-fold) increased risk for developing autopsy-confirmed cortical LBP compared to women; this is an observation replicated in many autopsy series. Our overarching hypothesis is that a particular microRNA (miRNA; miR-497) contributes to sexually-dimorphic DLB pathogenesis. In preliminary studies we made the following observations: miR-497 is expressed sexually dimorphically in human brain and in rat primary cultured neurons; miR-497 is enriched in human brains with LBP and in LBP- vulnerable brain areas; and, miR-497 expression in cultured cells alters alpha-SN and DJ-1/PARK7 expression. Our lab has expertise in both LBP and miRNAs which enable us to test the hypothesis that miR- 497 regulates alpha-SN expression and may influence LBP in a sexually dimorphic manner. Specific Aim 1: Test the hypothesis that miR-497 is sexually dimorphically expressed in human brain, and dysregulated in human brains with LBP. Proposed studies will represent the state of the art in miRNA profiling using miRNA microarrays to test for associations between miRNA expression and both LBP and gender status. Preliminary data indicate a systematic tendency for sexually dimorphic miR-497 to be dysregulated in brains with LBP and in human brain areas vulnerable to LBP. Specific Aim 2: Test the hypothesis that sexually dimorphic miR-497 regulates alpha-SN expression. Preliminary data indicate that miR-497 regulates alpha-SN. Primary rat neurons will be transduced with lentiviral vectors expressing miR-497 versus other control miRNAs to test the hypothesis that miR-497 regulates alpha-SN. Further experiments in these cells will query whether the regulation of alpha-SN by miR- 497 is direct or via an intermediate regulation of PARK7/DJ-1 gene. Following viral transduction with miR-497 and control miRNAs, we will determine the full list of miR-497 targets in cultured primary neurons. These mechanistic experiments will aid our ultimate goal of therapies to combat this currently untreatable disease. Public health significance: Understanding how sexually dimorphic miR-497 alters alpha-SN expression to induce sex-dimorphic pathology would be a major novel paradigm in neurochemistry with clinical/translational significance for both diagnostic and therapeutic strategies. The primary cel culture system will offer an experimental paradigm for testing novel methods of attenuating the dimorphic expression of miR-497 that drives alpha-SN expression.